1. Field of the Invention
The present invention relates to a data communication system capable of forming part of an integrated services digital network handling formatted data information channels between a plurality of subscribers. Each channel contains signalling and possibly low speed data information and is carried on a separate link comprising at least one high speed link for its subscriber. The signalling channel messages transmitted by these links are formatted, for example with the particular flag, message, frame check sequence, flag frames according to the international standard High Level Data Link Control (HDLC) protocol.
The data communication system interfaces with each individual subscriber link via a line circuit which separates the incoming data channels from the signal channels to forward the data channels to a digital exchange switch for connection to another subscriber, the line circuits being provided on line cards.
2. Description of Related Art
In a known system the signalling channel is converted from its initial format to some other format pertinent to the internal architecture of the exchange design by the individual provision at each line circuit of a commercially available HDLC chip and the provision at each line card of a microprocessor with RAM and ROM.
A disadvantage of the known system just described is the high cost and high power consumption involved in providing an individual HDLC chip at each line circuit, and message processing means including a microprocessor, RAM and ROM at each line card for handling the deformatted messages. An object of the present invention is to overcome this disadvantage.